1. Field of the Invention
The present invention relates to an apparatus for and a method of controlling the engine RPM (Revolutions Per Minute) in hydraulic construction equipment, and more particularly to such control apparatus and method being capable of detecting a neutral valve position corresponding to the idle state of the construction equipment and controlling the engine to drive at a low RPM while the construction equipment is in its idle state, thereby achieving a reduced noise generation and reduced fuel consumption.
2. Description of the Prior Art
Generally, numerous hydraulic construction equipment employ a device for automatically decreasing the engine RPM (namely, carrying out auto-deceleration) when the hydraulic construction equipment is not performing any operations such as operating a working member thereof, travelling or swinging.
A technique concerned with such auto-deceleration is disclosed in the Japanese Patent Publication No. 85-38561 filed on Sep. 2, 1985. In accordance with this technique, neutral positions of control levers for controlling the operations of working members, travelling or swinging are detected. When a certain period of time elapses after the detection of the neutral position of each control lever, the engine RPM is automatically decreased so that the engine can be driven at a low speed.
However, this system requires the use of a plurality of detection means for detecting respective neutral positions of the control levers. It also requires the use of a time measuring means (timer) so that the engine RPM can be decreased after a certain time has elapsed. As a result, this system has the disadvantage that a number of elements should be used. Furthermore, a series of operations for decreasing the engine RPM and then increasing the decreased engine RPM again are detected, based on specified positions of each control lever, respectively. However, such a detection method results in frequent malfunction. As a result, it is impossible to obtain flexibility in control. In other words, although the transition of the valve state (namely, the position of the valve spool) from the actuating state to the neutral state and vice versa should be accurately detected in terms of the point of time, it may not coincide with the corresponding shift of the control lever due to the tolerance of the valve block given upon machining the valve block.
Where the neutral valve state is determined, based on only the detection for the specified position of each control lever, therefore, malfunctions may occur frequently. Consequently, the conventional system has the disadvantage that auto-deceleration is carried out at a point of time when the auto-deceleration is unnecessary and another disadvantage that the recovery of the engine RPM for re-actuating the working members is delayed.